Electrical device



Oct. 8, 1940.

H. J. CRABBS ELECTRICAL DEVICE Filed Feb. 20, 1937 2 Sheets-Sheet 1 1 j 43 fg 43 49 K49- 4Z 42 4/ ,-21

INVENTOR /f'rberf Crabbs.

Patented Oct. 8, 19-40 2.2917333 ELECTRICAL DEVICE Herbert J. Crabbs, Wilkinsburg, Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Appucauen February zo, 1937ser1a1No. 126,878

21 Claims.

The invention relates to electrical devices in general, and more particularly to a high pressure contact securing means for electrical devices.

The engaging surfaces of the usual types of 5 contacts such as are used in switches, fuses and the like, are subject to the accumulation of foreign matter which eventually forms a lm of relatively high resistance on the surfaces, resulting in a high normal contact resistance and a l very undesirable heating action because of the poor contact.

In the case of switches and particularly knife type switches, the engaging contact surfaces require careful machining and grinding in when l new, as well as considerable maintenance in service. The switches also require frequent and careful contact pressure adjustment.

It is an object of the invention to provide a novel and improved contact pressure securing 80 means.

Another object of the invention is the provision of an improved contact pressure securing means for association with one or the other of two cooperating contact surfaces, for producing u a plurality of high pressure line contacts between the surfaces of the contact members.

Another object of the invention is the provision of an improved contact pressure securing means for association with one of two cooperat- 80 ing contact members for appreciably reducing the normal contact resistance between the members.

Another object of the invention is the provision of an electrical switch having a pair of cooperating relatively movable contacts with a 3`5 means for securing a plurality of high pressure line contacts between the engaging surfaces of the contacts.

Another object of the invention is the provision of an electrical switch having relatively mov- 40 able contacts with a contact pressure securing means which materially reduces the normal contact resistance and eliminates the necessity of careful machining or grinding in and contacting of the contact surfaces.

'l0 Another object of the invention is the provision of an electrical switch having relatively movable'contacts with a contact pressure securing means which materially reduces the normal contact resistance, and which permits ventilation 50 of the contact surfaces.

Another object of the invention is the provision of an electrical knife type switch havinga pair of switch blades, with a contact pressure securing means which permits the blades toV close 65 easily and which acts as a brush on closing and (Cl. o-166) as a scraper on opening of the blades to clean the contact surfaces of the blades.

Another object of the invention is the provision of an electrical knife switch embodying an improved Contact pressure securing means which reduces the normal contact resistance and also prevents the switch from being' blown open on heavy overloads or short circuits, thus eliminating the necessity of a latch or locking means.

Another object of the invention is the provision of a fuse having a fuse body and a removable fuse cartridge, with an improved means for securing a high contact pressure between the cooperating terminals or contacts of the body and cartridge.

Another object of the invention is the provision of an electric fuse having a fuse body and a removable fuse cartridge, with an improved contact pressure securing means'for the cooperating terminals or contacts of the body and cartridge which provides a plurality of high pressure line contacts between the surfaces of terminals or contacts of the body and cartridge.

Another object of the invention is the provision of a 4fuse having a fuse body and removable fuse cartridge or refill each provided with cooperating contacts, with an improved contact pressure securing means which materially reduces the normal contact resistance between the surfaces of the cooperating terminals.

The novel features that I consider characteristic of my invention are set forth in particular in the appended claims. The invention itself, however, both as to vstructure and operation together with additional objects and advantages thereof will best be understood from the following detailed description of a specific embodiment thereof when read in connection with the accompanying drawings, in which:

Figure 1 is a side elevational view of an electric switch embodying the features of my invention,

Fig. 2 is a plan view of the switch illustrated in Fig. 1,

Fig. 3 is a fragmentary sectional view of the contact portion of a switch embodying a modifled form of contact pressure securing means in which the edge twisted fins are arranged vertically instead'of horizontally as in the form shown in'Flgs. l and 2, the figure being taken on the line III-III of Fig. 4.

Fig. 4 is an end View of the modification shown in Fig. 3,

Fig. 5 is an enlarged fragmentary sectional View of the contact portion of the switch shown in Figs. 1 and 2 illustrating the horizontal arrangement of the edge twisted fins and taken on the line V-V of Fig. 6,

Fig. 6 is an end view of the switch contact portion'shown-in Fig. 5,

Fig. 7 is a side View partly in section and partly in elevation of an electric fuse embodying the features of my invention,

Fig. 8 is a view showing the contact pressure securing means embodied in the fuse shown in Fig. 7, before being bent into the form of a ring,

Fig. 9 is a vertical sectional view of a portion of the contact pressure securing means-shown in Fig. 8, taken on the line IX-IX of Fig. 8,

Fig. 10 is a plan view of the contact pressure securing means shown in Fig. 8; and,

Fig. 11 is an end view of the contact pressure securing means bent in the shape of a ring for use in the fuse.

Referring to the drawings, and particularly the Figures 1 and 2, a single pole, single throw disconnecting switch is illustrated which comprises, in general, a base I3, a pair of supporting insulator columns I5 and i1 mounted in spaced relation oni the base I3, a pivot tongue I9 and a stationary contact tongue 2I secured to metal cap pieces of the insulator columns I5 and I1 respectively, a multiple switch blade 23 pivotally supported on the pivot tongue I9, an operating eye 25 for operating the switch blade, and a contact pressure securing means indicated generally at 21.

The multiple switch blade assembly 23 comprises a pair of blades 29 pivoted on opposite sides of the pivot tongue I9 by means of a bolt 3I. A pair of spring washers 33 cooperate with the bolt 3I to press the blades 29 firmly against the sides of the pivot tongue I9. The blades 29 are secured for movement together and spaced apart by means of a spacer pin 35. 'I'he spacer pin is provided with reduced end portions 31 which project through each of the blades 29 and form shoulders with the body portion of the pin for engaging the inner sides of the blades.

The contact pressure securing means, which is shown more clearly in Figs. 5 and 6 comprises a pair of plates 39 of resilient conducting material. The plates 39 are loosely mounted on opposite sides of the stationary tongue contact 2I by means of bolts 4I; the tongue contact 2I being provided with recesses 42 on each side thereof for the reception of the plates 39. The bolts 4I are of such length that they permit limited lateral movement of the plates, as shown in Fig. 6.

Each of the plates 39 is provided with a plurality of parallel horizontally disposed ilns 43 formed integral with the plate by means of the perforations or cuts, as shown more clearly in Fig. 5. Each of the fins has a pair of parallel opposite sharp edges 45. The fins are twisted edgewise at an angle to the plate less than so that the opposite sharp edges of the fins project on opposite sides of' the plate 39 and resiliently engage the cooperating contact surfaces 41 and 49 of the blade and tongue contact respectively, when the switch is closed, as shown in Fig. 6. The sharp edges of the fins 43 of the plates 39 thus resiliently engage the cooperating contact surfaces of the blades 29 and the tongue 2| with a predetermined pressure in a plurality of line contacts.

The operating eye 25 comprises a bifurcated lever 5I the parallel legs 53 of which are shaped to form a pair of bell crank levers, as shown in Fig. 1. The legs 53 of the operating eye are means of the hook stick.

adapted to straddle the two blades 2l and are pivoted at their apex to the blades by means of a cross bolt 55. The cross bolt 55 is provided with a nut 51 which retains the operating eye 25 in pivotally mounted position on the blades 29 and also retains the spacer pin 35 in mounted position between the blades 29. The ends of the legs 53 of the operating eye are each provided with a projection 59 which cooperates with a cam projection il carried by the corresponding blade y29 so that the contact ends of the blades are forced inwardly toward the tongue contact I9 during the final closing movement of the operating eye. Counterclockwise rotation of the operating eye 25 is limited by the engagement of the legs 53 with the projecting ends 31 of the spacer pin 35.

The switch is adapted to be operated by means of a hook stick (not shown), the hooked end of which is inserted in the operating eye 25. The operation of the switch is briefly as follows. When the hook stick (not shown) is pulled to the left, the operating lever 5I is rotated in a counterclockwise direction to the dotted line p0- sition shown in Fig. 1. The movement of the operating lever in a counterclockwise direction permits the ends of the blade 29 to spring open to their normalV position, thus removing the greater part of the pressure exertedby the ends of the blades on the plates 39 and their ns 43. Continued pull of the hook stick rotates the blades 29 in a counterclockwise direction about the pivot pin 3| to the open circuit position. In closing the switch substantially the reverse action takes place. clockwise direction about their pivot pin 3| to the closed circuit position shown in Fig. l, by After the blades have been moved to their closed position continued movement of the hook stick causes rotation of the operating eye 25 in a clockwise direction. The clockwise rotation of the operating eye 25 causes the projections 59 at the ends of the legs 53 to engage the cam projections 6I carried by the blades 29, thus forcing the ends of the blades toward the tongue contact 2I. The nal closing movement of the eye thus causes the sharp edges of the i'lns to engage the cooperating contact surfaces of the tongue and blades with increased pressure.

The sharp edges 45 of the fins 43 cut lines olf contact into the cooperating contact surfaces of both the tongue contact and the blades, thus eliminating the necessary careful preliminary contacting and grinding in oi' the contact surfaces. 'I'he sharp edges of the fins cut through any film that may form on the contact surfaces producing a plurality of metal-to-metal line con# tacts on both the blades and the tongue thus materially reducing the normal contact resistance of the switch. The openings provided in the plates 39 by the-twisted fins provide for desirable ventilation of the contact surfaces.

The horizontal disposition of the fins prevents the switch from being blown open on heavy overloads or short circuit conditions by reason of the fact that when the switch is in the fully closed position any force tending to open the switch such as is produced by magnetic reaction on overload or short circuit merely causes the fin edges to be pressed more rmly into the contact surfaces of both the tongue and the blades; the greater the blow-out action the tighter the fin edges will engage the contact surfaces. The contact pressure securing means thus acts to securely lock the blades in closed circuit position,

The blades 29 are first moved in a.

eliminating the necessity of any latch or locking means for this purpose.

During the switch opening operation after the operating eye has been rotated counterclockwise to the dotted line position shown in Fig. l, the normal pressure exerted by the fins causes the outer edges thereof to exert a brush action on the inner contact surfaces 41 of the blades 29. The fins thus produce a desirable cleaning action on the contact surfaces of the blades.

Figs. 3 and 4 show a slightly modified form of contact pressure securing/means for use with the type of switch shown in Figs. 1 and 2. In this modification, the plates 39' which are of resilient conducting material, the same as in the embodiment shown in Figs. 1, 2, 5 and 6, are provided with a plurality of vertically disposed fins each having opposite parallel sharp edges which project on opposite sides of the plate and resiliently engage the cooperating contact surfaces of the tongue contact 2 and the blades 29'.

The operation and advantages of this form of contact pressure securing means are substantially similar to that of the pressure securing means illustrated in Figs. 5 and 6, except that the f'lns do not prevent the switch from being blown open as in the embodiment shown in'Figs. 1 and 2. Also the edges of the fins do not exert the brushing and scraping action described in connection with the pressure securing means illustrated in Figs. 5 and 6.

'I'he plates 39 in Figs. 3` and 4 are mounted for limited lateral movement in recesses provided in the tongue contact 2 I by means of bolts 4 I in the same manner and for the same purpose as has been described in connection with the embodiment shown in Figs. l and 2.

In this modification, the normal pressure exerted by the twisted fins which tends to move the plates 39' to their outer limits of movement causes the sharp edges of the fins to cut through any film which may form on the inner contact surfaces of the switch blades 29 during the latter part of the opening movement and during the first part of the closing movement of the switch. The sharp edges of the twisted ns 45 resiliently engage the cooperating contact surfaces of the contact tongue 2| and blades 29 with a high pressure to provide a plurality of metal-to-metal line contacts, thus materially reducing the normal contact resistance of th switch. The ns also provide adequate ventilation to the contact surfaces in the same manner as kwas described in connection with the embodiment shown in Figs. l, 2, 5 and 6.

A fuse is illustrated in Fig. '7 which embodies a conta-ct pressure securing means somewhat similar to the contact pressure securing means shown anddescribed in connection with the disconnecting switch.

The fuse includes a cylindrical fiber tube 65 having threaded ends 61 and 69, and two tubular end terminal members or contacts 1| and 13 which have internally threaded portions 15 and 11, for engaging the threaded ends 61 and 69 respectively of the cylindrical tube 65. The outer surface of each of the end terminals or contacts 1| and 13 are cylindrical in form and are utilized for engaging suitable jaw or spring contacts (not shown) for connecting the fuse in an electrical circuit. The inner end of the end contact 1| is provided with external threads 19 for supporting an internally threaded clamping ring 83. The end contact 13 is provided at its inner end with a flanged portion 85 having a circular groove B1 formed therein. tube 82 is held in clamped position on the tube 65 by means of the ring 83 and the grooved flange 85, as shown in Fig. 7.

A fuse cartridge indicated generally at 89 is removably mounted in the tube 65 and held in position therein by means of a threaded ring 9| which engages internal threads provided in vthe enlarged end of the terminal or contact 1|. The right-hand end of the fuse cartridge engages a shoulder 93 formed in the end termina-l or contact 13.

The fuse cartridge 89 includes a refill element 95 provided with a cylindrical end contact 91 for cooperating with the internal cylindrical contact surface 99101' the end terminal or contact 1| of the tube 65. The refill element 95 is of the same general type and structure as the refill element shown and described in Patent No. 2,044,226 to Herbert L. Rawlins, issued June 16, 1936, and assigned to the assignee of this invention, the particular internal structure and mechanism of the fuse refill are not an important feature of the invention and for the details of structure and operation of the rell, reference may be made to the above referred to patent.

The right-hand contact of the fuse cartridge 89 comprises a cylindrical tube IOI of conducting material which is secured to the refill element 95 by a threaded connection indicated generally at |03. The cylindrical contact surface of the outer end of the contact |0| is adapted to cooperate with the internal contact surface |05 of the end terminal or contact 13 of the tube 65. The fuse refill 95 includes an insulating itube 96 enclosing a fusible element (not shown) which is electrically connected to the end terminals 91 and |0| on the ends of the insulating tube of the fuse cartridge 89.

A contact pressure securing means |01 is provided for the cooperating contacts 1l and 91, and 13 and |0I, at each end of the fuse,

The contact pressure securing means comprising a plate or strip |09 of resilient conducting material bent in the form of a split ring, is shown in Fig. 11. The plate |09 is provided with a plurality of parallel fins formed integral therewith by a plurality of perforations or cuts through the plates, as shown in Fig. 8. Each of the fins is provided with a pair of opposite parallel 'sharp edges I|3 and the fins are twisted edgewise, so that the sharp edges thereof project on opposite sides of the plate or strip |09, as shown ln Figs. 10 and 11.

Each of the contacts 1| and 13 is provided with a circular groove or recess ||5 for the reception of the contact pressure securing means |01.

The rings |09 are tensioned by compressing their ends ||1 together, and inserted in the recesses ||5 provided therefor in the contacts 1| and 13. After insertion, the natural resiliency of the strip or plate |09 expands the rings so that the outer sharp edges ||3 of the ns resiliently engage the inner contact surfaces 99 and |05 of the contacts 1| and 13 with a predetermined pressure and in a plurality of line contacts. When the fuse cartridge 99 is inserted within the fuse body 65, the contacts 91 and |0l are engaged by the sharp inner edges ||3 of the fins formed in the rings |09. The radial distance between the fin edges |I3 is slightly greater than the radial distance between the inner cylindrical contact surfaces of the contacts 1| and 13, and the cooperating external cylindrical contact surfaces of the contacts 91 and A cylindrical glass lili, so that the fin edges H3 engage the cooperating contact surfaces with a predetermined high pressure and in a plurality of line contacts, thus securing a plurality of metal-to-nietal line contacts and materially reducing the normal contact resistance of the fuse. During insertion and removal of the fuse cartridge 89, the internal sharp edges H3 of the fins III cut through any film or foreign matter that may exist on the surfaces of the contacts 91 and IUI.

The contact pressure securing means, has been shown in connection with a particular form of fuse structure for illustrative purposes only. It will be understood that the contact pressure securing means, either as shown, or with slight modifications, is applicable to various other types of fuses or electrical devices provided with separable cooperating contact surfaces.

While I have shown and described the invention in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details thereof may be made without departing from the spirit of the invention. I desire, therefore, that the invention be limited only by reasonable construction of the appended claims and by the prior art.

I claim as my invention:

l. A contact pressure securing means for an electrical device having cooperating separable contact surfaces comprising, a member of conducting material provided With a plurality of parallel fins each having ends integral with said member and having opposite sharp side edges, said fins being twisted so that the opposite side edges of each fin project on opposite sides of said member for engaging the cooperating contact Surfaces.

2. A contact pressure securing means for an electrical device having cooperating separable contact surfaces comprisingY a member of conducting material provided with a plurality of fins formed integral therewith each having opposite sharp side edges and each twisted so that its opposite side edges project on opposite sides of said member for engagement with the cooperating contact surfaces.

3. A contact pressure 'securing meansrfor an electrical device having cooperating separable contacts comprising, a plate of resilient conducting material provided with a plurality of sharp edged resilient projections formed integral therewith and bent so that a plurality of said sharp edges project from each side of said plate for resilient engagement with the contact surfaces of said contacts.

4. A contact pressure securing means for an electrical device having cooperating separable contact surfaces, comprising a member of resilient conducting material provided with a plurality of fins formed integral therewith by a plurality of spaced parallel cuts through said member and within the boundaries thereof, said fins being twisted at an angle less than a right angle to said member so that their opposite edges project on opposite sides of said member for engaging said contact surfaces with a plurality of line contacts.

5. A contact pressure securing means for an electrical device provided with cooperating separable contact surfaces comprising a plate of resilient conducting material provided with a plurality of fins formed integral therewith each having opposite parallel sharp side edges, said fins each being twisted so that the opposite side edges of each tin project on opposite sides of said member for engaging said contact surfaces with a plurality of line contacts.

6. A contact pressure securing means for an electrical device provided with cooperating separable contact surfaces comprising a plate of resilient conducting material perforated to form a plurality of sharp edged projections bent so that a plurality of said sharp edges project from each side of said plate for engaging said contact surfaces.

7. In an electrical device provided with separable contacts having cooperating contact surfaces. the combination of a plate of resilient conducting material disposed adjacent one of said contact surfaces, said plate having a plurality of sharp edged projections formed integral therewith and bent so that a plurality of said sharp edges project from each side ot said plate for resiliently engaging said cooperating contact surfaces to provide a good electrical contact between said contacts.

8. In an electrical device having separable cooperating contact surfaces, the combination of a member of resilient conducting material provided with a plurality of parallel integral fins each having opposite sharp side edges. said ns being twisted so that the opposite side edges of each project on opposite sides of said member for resiliently engaging said contact surfaces, means loosely mounting said member with the sharp side edges of the fins projecting from one side of said member in engagement with one of said contact surfaces so that when said other contact surface is brought into circuit closing position the opposite sharp side edges of said fins will resiliently engage said contact surfaces with a predetermined pressure.

9. In an electrical device having separable cooperating contact surfaces, the combination of a contact pressure securing means comprising a plate of resilient conducting material provided with a plurality of parallel fins formed integral therewith each having opposite parallel sharp side edges, said ns being bent at an angle to said plate so that the opposite side edges of each iin project on opposite sides of said member, means mounting said member with the side edges of said fins which project from one side of said plate in contact with one of said contact surfaces so that when said surfaces are in closed circuit position, the opposite side edges of said fins resiliently engage the cooperating contact surfaces with a predetermined pressure in a plurality of line contacts.

10. In an electrical device having separable cooperating contact surfaces, the combination of a contact pressure securing means comprising a member of resilient conducting material provided with a plurality of parallel fins formed integral therewith each having opposite parallel sharp side edges, said fins being twisted at an angle less than a right angle to said member so that the opposite side edges of each fin project on opposite sides of said member, means mounting said member for limited movement adjacent one of vsaid contact surfaces so that when said contact surfaces are separated the edges of said fins on one side of said member resiliently engage said one contact surface, and when said contact surfaces are in closed circuit position the opposite side edges of said fins resiliently engage both said contact surfaces with a high pressure in a plurality of line contacts.

11. In a circuit controlling device, a stationary contact and a movable contact therefor each having cooperating contact surfaces, a contact pressure securing means comprising a plate of resilient, conducting material provided with a plurality of fins formed integral therewith each having opposite parallel sharp side edges, said ns being twisted so that the opposite side edges of'each fin project on opposite sides of said plate, means mounting said plate for limited lateral movement adjacent one of said contact surfaces so that the side edges of said fins on one side of said plate resiliently engage said one contact surface when said device is in open circuit position, and so that opposite side edges of each iin resiliently engage both of said contact surfaces with a high pressure in a plurality of line contacts when said device is in closed circuit position. l

l2. In a circuit controlling device, a stationary contact and a movable contact therefor each havin,J cooperating contact surfaces, a contact pressure securing means comprising a plate of resilient conducting material provided with a plurality of integral parallel sharp edged-fins formed integral therewith, said fins being bent so that a plurality of said sharp edges project from each side ofsaid plate, means mounting said plate for limited lateral movement adjacent one of said contact surfaces so that when said device is in closed circuit position the edges of said fins resiliently engage both said contact surfaces with a high pressure and in a plurality of line contacts.

13. In a vertical break electric circuit controlling device, a stationary contact and a movable contact therefor, each having cooperating contact surfaces, a contact pressure securing means comprising a plate of resilient conducting material provided with a plurality of integral parallel sharp edged fins, bent so that a plurality of said sharp edges project from each side of said plate, means mounting said plate for-limited lateral movement adjacent one of said contact surfaces with said fins disposed vertically so that when said device is in closed circuit position the edges cf said fins resiliently engage both said contact surfaces with a high pressure and in a plurality of line contacts.

14. In a vertical break circuit controlling device, a stationary contact means and a movable contact means each having a plurality of cooperating contact surfaces, a contact pressure securing means comprising a pair of plates of resilient conducting material yeach provided with a plurality of parallel sharp edged fins bent to project on opposite sides of said plate, means mounting said plates for limited lateral movement adjacent certain of said Contact surfaces so that when said device is in closed circuit position the edges of said ns resiliently engage the contact surfaces of said stationary contact means and said movable contact means with a plurality of line contacts, means operable during a switch closing operation for successively moving said movable contact means in proximity to said stationary contact means and then relatively moving the cooperating contact surfaces toward one another to increase the pressure of engagement of said fin edges with said contact surfaces.

15. In a vertical break electric circuit controlling device, a stationary contact means and a movable contact means therefor each having a plurality of cooperating contact surfaces, a contact pressure securing means comprising a pair of plates of resilient conducting material each provided with a plurality of parallel sharp edged fins bent to project on opposite sides of said plate, means mounting said plates for limited lateral movement adjacent certain of said contact surfaces so that when said device is in closed circuit position the edges of said fins resliently engage the contact surfaces of said movable contact means and said stationary contact means with a plurality of line contacts, means operable during a circuit closing operation for successively moving said movable contact means in proximity to said stationary contact means and then relatively moving the cooperating contact surfaces toward one another to increase the pressure of engagement of said fin edges with said contact surfaces, said fins being so disposed that they prevent the device from being blown open on short circuit or heavy overload.

i6. In a vertical break electric circuit controllnig device, a stationary contact means and a movable contact means therefor each having a plurality of cooperating contact surfaces, a contact pressure securing means comprising a pair of plates of resilient conducting material each provided with a plurality of parallel sharp edged fins bent to project on opposite sides of said plate, means mounting said plates for limited lateral movement adjacent certain of said contact surfaces so that when said device is in closed circuit position the edges of said fins resiliently. engage the Contact surfaces of said stationary contact means and said movable contact means with a plurality of line contacts, means operable during a circuit closing operation for successively moving said movable contact means in proximity to said stationary contact means and then relatively moving the cooperating contact surfaces toward one another to increase the pressure of engagement of said fin edges with said contact surfaces, said ns being vertically disposed for engaging the contact surfaces of said movable contact means in lines substantially parallel to the path of final closing movement of the movable contact surfaces.

17. In an electric circuit controlling device, a body member having a contact adjacent each end, a circuit controlling member removably associated With said body and 'having a contact adjacent each end for cooperating with the contacts of said body, the contacts of said body and the contacts of said circuiti/controlling member having cooperating contact surfaces, in combination, Contact pressure securing means comprising a plate of resilient conducting material disposed between the cooperating contact surfaces adjacent each end of the device, said conducting plates each provided with a plurality of sharp edged projections formed integral therewith and bent so that the edges project on opposite sides of said plate and resiliently engage the cooperating contact surfaces with a predetermined hi'th pressure.

18. In an electric circuit controlling device, a body member having a contact adjacent each end, a circuit controlling member removably associated with said body and having a contact adjacent each end for cooperating with the contacts of said body, the contacts of said body and the contacts of said circuit controlling member having cooperating contact surfaces, in combination, contact pressure securing means comprising a member of resilient conducting material disposed between the cooperating contact surfaces adjacent each end of the device, said conducting members each provided with a plurality of parallel fins formed integral therewith each having opposite parallel sharp side edges, said fins being twisted so that the opposite side edges of each nn project on opposite sides of said member and resiliently engage said cooperating contact surfaces with a predetermined high pressure in a plurality of line contacts.

19. In an electric circuit controlling device, a hollow body member provided with a contact adjacent each end having an internal cylindrical contact surface, a current carrying member removably disposed in said body member provided with a contact adjacent each end having an external cylindrical contact surface for cooperating with the internal contact surface of the corresponding body contact, a circuit controlling element carried by said current carrying member and electrically connected to the contacts thereof, contact pressure securing means comprising a. split ring of resilient conducting material disposed between the cooperating cylindrical contact surfaces adjacent each end of the device, said rings each provided with a plurality of parallel ns formed integral therewith each having opposite parallel sharp side edges, said fins being twisted so that the opposite side edges of each iin project on opposite sides of said ring and resiliently engage said cooperating contact surfaces with a predetermined high pressure in a plurality of line contacts.

20, In an electrical device having cooperating contact surfaces, the combination of a contact pressure securing means comprising a member of resilient conducting material disposed between said contact surfaces and having an area substantially equal to the area of at least one of said contact surfaces, said member being provided with a plurality of integral projecting portions projecting from each side of said member for resiliently engaging both contact surfaces to provide a good current connection between said surfaces, a plurality of said integral projections of said member engaging each contact surface.

21. A contact means comprising a member of conducting material provided with a plurality of parallel fins each having its ends integral with said member and having opposite parallel side edges, said fins being twisted about their longitudinal axes so that the opposite side edges of each iin project on opposite sides of said member.

HERBERT J. CRABBS. 

